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Hearing aids, at their most basic level, may be described as amplifiers with adjustments (e.g. volume, tone, MPO). For conventional hearing aids these adjustments are often made with trimmers (very small variable resistors). Alternatively, because of size limitations, the hearing aid manufacturer often presets the adjustments. In any case, as hearing aids become ever smaller and as the number of possible adjustments increases due to AGC, multi-band circuitry and other enhancements, it has become nearly impossible to fit all the required adjustments in a hearing aid that will be of a size acceptable to the patient.
In an attempt to solve this problem, programmable hearing aids were developed. Originally, programmable hearing aids were analog hearing aids with xe2x80x9cdigital trimmers.xe2x80x9d In other words, early programmable hearing aids had some form of trimmer that could be controlled by some form of memory that could be programmed by some external apparatus. While there are substantial differences in circuitry between the earlier xe2x80x9cprogrammable analogxe2x80x9d hearing aids and the later xe2x80x9ctrue digitalxe2x80x9d hearing aids, both of them require xe2x80x9cprogrammingxe2x80x9d and will be considered together under the name xe2x80x9cprogrammable hearing aidxe2x80x9d.
Programming a programmable hearing aid generally involves two-way communication. Specifically, a programming system enables the reading of the current settings of the hearing aid as well as the writing of new settings to the hearing aid. Other schemes have been employed involving one-way communication, such as, for example, radio frequency, optical or acoustic programming, but to date have been mostly used for changing a hearing aid""s settings from one previously programmed condition to an alternate previously programmed condition.
Wired programming has existed in many forms from a high of five wires to a low of two. The most common current system was invented by Starkey and uses 3 wires (Ground, Power and Data). In this system, the data line is controlled primarily by the hearing aid in a six segment per bit protocol. It is the programming instrument""s responsibility to adapt, within limits, to the timing of the hearing aid. An example of a circuit using this protocol is Etymotic Research ER-102 Digital ScrewDriver. The main disadvantage of a three-wire system is that a connector is required. In the ever-smaller hearing aid, a connector, no matter how small, is still a mechanical disadvantage. It is also a cost disadvantage.
One solution to this problem has been developed and is being marketed by RTI. RTI""s solution is to modify the faceplate battery drawer from a two-wire configuration to a four-wire configuration. They then provide appropriately sized xe2x80x9cbattery pillsxe2x80x99 that mate with the modified battery drawer. This solves the mechanical problem posed by an additional connector on the faceplate. However, the multi-wire battery pill is inherently fragile. It is necessary to remove the battery door in order to insert the battery pill.
A two-wire protocol, using a conventional battery pill is desirable for many reasons. For example, two-wire battery pills are much more rugged, do not require battery door removal, are widely available, match faceplates from all manufacturers and require no additional wiring in the hearing aid from the faceplate to the circuit.
A two-wire protocol was created by ReSound and exists in the public domain but has found little favor. In the ReSound protocol, information is sent to the hearing aid by the programming instrument using voltage pulses (from 1.25 to 2.50 Volts). Information is sent to the programming instrument from the hearing aid using current pulses (additional 1 mA drain). The protocol is a pulse width modulated scheme operating at 1 kHz. xe2x80x9c0""sxe2x80x9d are sent ⅓rd high and ⅔rd low. xe2x80x9c1""sxe2x80x9d are sent ⅔rd high and ⅓rd low. This system has several disadvantages. First, it has no synchronization capability. This requires that the frequency of the hearing aid and the frequency of the programming instrument be very closely matched. Such requirement forces the hearing aid to be more complex, and therefore both more costly and larger. A second and far more important disadvantage is that the system can only work with Class B receivers and not with the more common Class D receivers. More specifically, Class D receivers require a 2.2 uF bypass capacitor across their power supply terminals, and Class B receivers do not. This bypass capacitor alone requires that the programming instrument source/sink in excess of 25 mA in order to send data at the relatively slow 1 kHz rate. Currently, common programming instruments are not capable of doing that.
Further limitations and disadvantages of conventional and traditional systems will become apparent to one of skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.
These and other problems in the prior art are addressed by the hearing aid of the present invention, which in one embodiment, generally comprises a receiver and a bypass capacitor (such as commonly found with Class D receivers). Circuitry is included that disconnects the bypass capacitor and, if desired, other hearing aid components during a hearing aid programming operation. The circuitry also reconnects the bypass capacitor (and other hearing aid components, if disconnected) after the hearing aid programming operation. In other words, the circuitry switches between a normal hearing aid operating mode in which the bypass capacitor is connected and a programming mode in which the bypass capacitor is disconnected.
In one embodiment, the circuitry includes a comparator and a switch. The switch is opened and closed in response to the input voltage rising above and falling below a predetermined threshold value, which may be, for example, 1.5 volts. When the input voltage is below the threshold value, the hearing aid operates in a normal manner at a first voltage, such as, for example 1.25 volts. When the input voltage is above the threshold value, the hearing aid operates in a programming mode. In the programming mode, the hearing aid receives logic data from a programmer at second and third voltages, which may be, for example, approximately 1.6 and 2.5 volts, respectively. In other words, the hearing aid of the present invention uses three voltage levels for operation in both the normal and programming modes, namely, one for normal operation, a second for logic low signals and a third for logic high signals.
The present invention enables use of a two-wire configuration and two-way communication for programmable hearing aids having non-Class B receivers, as well as faster transmission rates.
In addition, the circuitry of the present invention further utilizes a protocol that enables an external programmer (i.e., programming device or system) to automatically determine and track the hearing aid data transfer rate as well as the make and model of the hearing aid.